Four of the 10 most marginal seats changed political colours in the 2017 election, as a number of incumbents stood aside and new candidates reinvigorated contests.

The closest race that changed hands was Ohariu, where United Future's Peter Dunne retired just one month before the election.

The National Party had an electoral accommodation with Dunne, and campaign manager Steven Joyce has said that he wished Dunne had withdrawn earlier, giving National candidate Brett Hudson more time to campaign; Labour's Greg O'Connor beat Hudson by only 1051 votes.

In contrast Tamati Coffey had almost a year to campaign after he was selected to run as the Labour candidate in the strategic seat of Waiariki in October 2016. Coffey defeated Maori Party co-leader Te Ururoa Flavell, whose party failed to return to Parliament.

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Labour candidate Willow-Jean Prime may have been the difference in the Northland result, where New Zealand First leader Winston Peters lost the seat he had won in the 2015 byelection. Prime did not actively campaign in 2015 and won only 1380 votes, far fewer than the 8599 votes she won in the September election.

National's Chris Bishop turned a 709-vote loss in Hutt South in 2014 to a 1530-vote win in 2017 over Labour's Ginny Anderson, following Labour incumbent Trevor Mallard's decision to stand as a list MP. It is the first time National has held the seat since it was created in 1996.

Other close races featured new candidates that retained seats for their respective parties.

In Maungakiekie, where National's Sam Lotu-Iga retired, National's Denise Lee won a 2157 majority over Labour's Priyanca Radhakrishnan - almost 2000 votes fewer than the number of votes that Green candidate Chloe Swarbrick won.

Labour's Deborah Russell defeated National's Paulo Garcia in New Lynn, a seat vacated by former Labour leader David Cunliffe, but where National had won the party vote in 2014. The party vote swung back to Labour with a narrow 307-vote majority in 2017.

National's Lawrence Yule managed to hold Tukituki, where National incumbent Craig Foss retired, though established Labour candidate Anna Lorck, who also ran in 2014, substantially closed the gap.

In the country's most marginal seat, Labour's Adrian Rurawhe again won Te Tai Hauauru, defeating a strong challenge from former rugby league star and Maori Party candidate Howie Tamati.

National's Harete Hipango retained Whanganui following the retirement of National incumbent Chester Borrows.

Nine of the 10 largest majorities went to National candidates, the largest being the 19,639 margin won by Selwyn MP Amy Adams. The only Labour candidate to make the top 10 was leader Jacinda Ardern, who won Mt Albert with a 15,264 margin.

Ardern had previously failed to win Auckland Central, where National's Nikki Kaye extended her narrow majority from 600 over Ardern in 2014 to 1581 over Labour's Helen White.

Four of the top 10 largest candidate majorities went to new MPs standing in National safe havens: Erica Stanford in East Coast Bays (previously held by Murray McCully), Tim van de Molen in Waikato (previously held by Lindsay Tisch), Simeon Brown in Pakuranga (previously held by Maurice Williamson), and Chris Penk in Helensville (previously held by John Key).

National also took nine of the top 10 electorates with the biggest party vote majority, mostly in affluent areas around Auckland: Hunua, Rodney, Tamaki, East Coast Bays, Epsom and Pakuranga.

Clutha-Southland also made the list, despite the controversy surrounding former MP Todd Barclay, and the handling of the matter by party leader Bill English. National MP Hamish Walker won the seat with a 14,354 majority, though the share of the party vote fell from 63 per cent in 2014 to 59 per cent in 2017.